Bonding Coordination Defects in Selenium

Abstract

A great variety of experimental phenomena have been attributed to under- or over-coordinated sites in chalcogenide glasses. The electronic structure of these bonding coordination defects has proven to be an interesting but very difficult theoretical problem. We have recently succeeded in developing a realistic approach which delivers new information about the origin, character, energy, and localization of the electronic defect statesp]. We calculate the electronic structure of bond coordination defects in selenium using self-consistent pseudopotential (SCPSP) and tight binding (TB) techniques. The SCPSP is applied to periodic ‘superlattice’ configurations containing defects; a TB model is then fitted to these results. The simpler TB Hamiltonian is applied to more realistic non-periodic structures, for which it can still be solved exactly. The TB model includes nearest-neighbor interactions and overlaps between s and p valence orbitais; in addition, we find we must include ~1.2 eV shifts in the diagonal Hamiltonian matrix elements on 1-fold and 3-fold sites. The origin of these shifts will be discussed shortly.